More generally, the invention relates to the field of electric motors having permanent magnets such as brushless, electronically commutated DC motors and other permanent magnet motors, the motor according to the invention being configured as either an inner rotor motor or an outer rotor motor. In general, inner rotor motors consist of a rotor arrangement which is mounted onto a motor shaft and includes one or more permanent magnets, as well as a stator arrangement having a stator core which is constructed, for example, from metal laminations and carries windings.
In the case of inner rotor motors, the rotor arrangement is coaxially inserted into the stator arrangement and rotatably journaled with respect to the stator arrangement using appropriate bearings.
For outer rotor motors, the stator is fixed to the likewise stationary shaft. The teeth of the stator aligned radially outwards are enclosed by the rotor arrangement that is rotatably journaled with respect to the stator arrangement using appropriate bearings.
FIG. 3 shows the basic construction of an electric inner rotor motor for the purpose of explaining the background of the invention. The motor comprises a housing 114 in which a stator arrangement 118, a rotor arrangement 116 as well as bearings 126, 128 to rotatably journal the rotor arrangement are accommodated. The stator arrangement 118 comprises stacked metal laminations 155 and windings 160 and defines an inner space into which the rotor arrangement 116 can be inserted. The rotor arrangement 116 includes the shaft 110, a back iron yoke 112 and permanent magnets 122. The bearings 126, 128 supporting the rotor arrangement can be integrated into a flange 124 in the motor housing 114. As mentioned above, FIG. 3 serves to explain the basic construction of an electric motor where the stator according to the invention can be configured as either an inner rotor motor or an outer rotor motor. In the case of an outer rotor motor, the stator is mounted onto the shaft and is enclosed by the rotor.
FIG. 1 shows a schematic sectional view through an outer rotor motor according to the prior art.
The electric motor schematically illustrated in FIG. 1 comprises a housing 10 in which a stator arrangement 12 and a rotor arrangement 14 are accommodated. The stator arrangement 12 is built up, for example, from a stack of stamped metal laminations having stator teeth 16 and stator slots 18 formed between the stator teeth 16. The stator slots 18 are open towards the outer circumference of the stator arrangement 12 and the stator arrangement 12 is entirely enclosed by the rotor arrangement 14. The rotor arrangement 14 comprises a rotor body 20 in which permanent magnets 22 are embedded. The direction of magnetization of the permanent magnets is shown by arrows in FIG. 1 (north→south).
In the excited permanent magnetic electric motor illustrated in FIG. 1, the coils or stator windings 24 are wound about stator teeth 16 which form “electromagnetic poles” according to the direction of current. The illustrated electric motor is also referred to as a slotted motor.
In many cases slotted motors are designed so that the stator windings are wound about one stator tooth 16 alone. This is called one-tooth or concentrated winding. FIG. 1 shows a typical design for a stator having 12 slots, where it is easy to see from FIG. 1 that one half of two stator windings or coils 24 are accommodated in each stator slot 18. In FIG. 1, the stator windings 24 having different phases are designated by different hatchings, the coils 24 of a first phase being indicated by A, of a second phase by B and a third phase by C.
For specific combinations of the number of pole pairs of the rotor arrangement 14 and the number of slots of the stator arrangement 12, the halves of two coils 24 lying within one stator slot may even belong to the same phase. This also applies to the combination illustrated in FIG. 1 having 12 stator slots and 14 poles. The winding pattern for the electric motor illustrated in FIG. 1 can be laid out as follows:
Slot no.123456789101112Stator windingAabBCcaABbcC
In this table, the winding direction is designated by capital and small letters and thus indicates whether the winding belonging to the respective phase directs the current into the slot or leads it away from the slot. It can also be said that this goes to indicate whether the winding and thus the direction of current is arranged clockwise or anticlockwise about the stator tooth concerned.
The stator windings 24 of the stator arrangement illustrated in FIG. 1 are wound using Flyer technology. Here, the wires of the stator windings are led through the slot openings between two stator teeth 16 and held under tension in such a way that they are engaged on the respective stator tooth 16. Accordingly, this means that the space available for the stator winding cannot be fully exploited.
Based on the prior art as described above, it is the object of the invention to provide a stator for an electric motor which makes it possible for an improved space factor to be achieved and makes the insertion of the stator windings into the stator slots easier.